The present invention relates to a mechanism for attaching a tracking system component to an instrument. More particularly, certain embodiments of the present invention relate to a universal attachment mechanism for attaching a surgical tracking localizer to a cylindrical surgical instruments of varying diameters.
During surgical operations, it is beneficial to be able to track the direction, trajectory and distal tip of a surgical instrument, such as a drill bit, into a patient's body in order to ensure that the instrument is directed into the appropriate point in the body. Therefore, surgical tracking systems have been developed that are able to display and monitor the direction, trajectory and distal tip of a surgical instrument relative to an image of the patient's body.
One system used for surgical tracking is an electromagnetic tracking system. In a typical electromagnetic tracking system, the area of the patient's body where surgery is to take place is imaged using an imaging technology such as the MRI, ultrasound, X-ray, CT scan or any other appropriate imaging device. The scanned images are stored in a computer system and are displayed on a screen during the surgical procedure. Alternatively, some systems, known generally as imageless systems, use a computer model in place of the scanned image. Data points are taken from the actual patient in the operating room and the model is morphed to provide an image representing the actual patient. A transmitter that emits an electromagnetic field is then secured to the patient's body proximate the area of the patient's body where surgery is to take place in a fixed and known position to the surgical site. The instrument that is to be tracked during surgery has a receiver attached thereto that receives the electromagnetic signals from the transmitter. The transmitter and receiver are both connected to communicate with the computer that displays the image. The computer translates the location of the transmitter to an equivalent point on the image. Then, by monitoring the signals sent from the transmitter to the receiver as the instrument is used in surgery, the computer is able to track the movement of the instrument relative to the transmitter, and thus the surgical site, and transpose the movement to the image. Therefore, medical personnel may closely track the positioning and progress of the instrument within the patient's body during surgery by examining the image.
Alternatively, in some electromagnetic systems, a receiver is placed on the patient and the instrument, and a field transmitter is placed proximate the patient. The receivers and transmitter are connected to the computer, and the computer is then able to track the movements of the instrument on an image similarly to the system using just a single receiver.
There are other surgical tracking systems besides electromagnetic tracking systems, such as optical tracking systems. Optical tracking systems typically use light emitting diodes (LEDs) that are attached to the surgical instrument and to the body portion of the patient on which the surgical procedure is to be performed. The LEDs are tracked by a camera unit (sometimes referred to as a digitizer). The output of the camera unit is used by the computer to recreate the movement of the instrument on the image.
In order for a surgical tracking system to work, the tracking device attached to the instrument, whether it be a receiver, transmitter or an LED, must be calibrated with the trajectory and distal tip of the instrument. When the trajectory and distal tip of the instrument are known relative to the tracking device, then the computer can effectively determine the location of the instrument. Calibration of a tracking device is greatly simplified by placing the device a constant distance from the trajectory (the centerline) of the rotating shaft of the instrument being tracked. In this fashion, a simple calibration would be required to calibrate the position of the distal tip of the instrument. If the trajectory of the cylindrical tool is in a known relationship to the tracking device, then only calibration of the instrument's distal tip is required for fully determining the location of the instrument. Methods of accurately locating the distal tip are well known in the art.
The tracking device may be custom-integrated into the surgical instrument, however, such a practice involves considerable development costs and time to integrate each individual application. Additionally, many new surgical applications require tracking of cylindrical tools of varying diameters such as awls, drills, drill guides, probes, and various drivers. Therefore, universal systems for calibrating the trajectory and distal tip of a tool have been developed.
For example, one system used for tracking an interchangeable rotating cylindrical instrument, such as a drill bit, is the tool calibrator described in U.S. Pat. No. 5,987,960 to Messner. In Messner, there are tracking devices on the instrument handle and on two interlocking blocks. The interlocked blocks have oppositely aligned V-shaped grooves that receive the instrument head therein such that the tracking devices on the blocks are a known distance from the centerline of the instrument. Thus, the tracking devices on the blocks can communicate with a computer system to calculate the trajectory of the instrument. The instrument has a first point that is in a known position relative to the tracking devices on the instrument. One of the blocks has a second point that is in a known position relative to the tracking devices on the blocks and a flat surface on the block. The distal tip of the instrument is positioned to engage the flat surface on the block, then the tracking devices on the instrument and the blocks communicate with the computer to calculate the position of the distal point with respect to a reference frame of the instrument.
However, the calibration system of Messner suffers from its own drawbacks. There is the added expense of integrating tracking devices onto the instrument handle in addition to having tracking devices on the blocks. Additionally, it is a cumbersome practice to have to attach the blocks to each new instrument head used during the surgery, calibrate the instrument with the blocks, and then remove the blocks. Furthermore, the Messner system cannot be used with an instrument having an attachment at the distal tip.
Therefore, a need exists for an improved attachment mechanism for attaching a tracking device to any number of different cylindrical instruments.